Some printing or imaging machines using an imaging or transfer drum require the application of a liquid intermediate transfer layer. For instance in some liquid ink jet printers, a print head ejects drops of ink onto the liquid intermediate transfer layer to form an image thereon. The receiving substrate, such as paper, is brought into contact with the drum, and more particularly with the transfer layer, so that the ink is transferred from the layer onto the substrate. The intermediate transfer layer is thus formed of a material, such as a release oil, that holds the ink drops as the drum rotates but readily releases the drops onto the receiving substrate as the substrate passes between the transfer drum and an opposing pressure roll.
Imaging or printing machines using a liquid intermediate transfer layer thus require some sort of applicator assembly for metering the fluid onto the drum surface. One such assembly includes a felt wicking pad that is continuously impregnated with a liquid, such as a release oil. The wicking pad contacts the imaging surface of the drum to transfer the liquid onto the surface of the drum. Excess liquid is skimmed off the drum surface by a downstream wiper blade.
Any element contacting the rotating drum is susceptible to contamination from ink dots, paper dust, clay and the like. The contaminations build up on the contacting element until its performance is significantly degraded, which can ultimately lead to compromised images on the receiving substrate. One school of thought has suggested that increasing the supply or release agent or oil to the surface of the rotating drum will reduce the propensity for contaminants to build up on the contacting elements, such as the wiper blade. The high oil supply rates necessary to achieve this beneficial result can be problematic for traditional wicking systems. The wicking pad relies upon internal capillary action to convey the oil from the source to the application edge of the pad. In most wicking pads, the capillary capability of the pad is limited and insufficient to achieve the necessary oil supply rates. Moreover, over time the capillaries of the wicking pad can become clogged with contaminants extracted from the rotating drum as well as from the liquid source.
High speed imaging and printing requires high supply rates for the liquid intermediate transfer layer onto a high speed rotating drum. The necessary high supply rates are extremely taxing to the current conventional wicking pad technology. Moreover, the presence of contaminants in any imaging or printing system means that the applicator assembly components will require more frequent cleaning as greater numbers of image transfers are performed. Eventually, cleaning of the applicator assembly components is insufficient to restore the performance of the applicator assembly, requiring replacement of the entire assembly.
Consequently, there is a need for an applicator assembly that can easily handle very high throughput systems, without the need for frequent cleaning or replacement.